When to Go
The best time to go when nobody else is on the lake so that you can hog all the best skiing water. You can tell it's good water for skiing because it has a lot of moss, driftwood, dead fish, and other icky/painful things floating on top of it. The very best times are weekdays at 6am and weekends at 4am.

Preparation
Boating takes some serious preparatory work. Make sure your parents get up early enough to get it all done. This involves washing the boat, getting it hooked up to your car/truck/bicycle, and making sandwiches. Sandwiches are the single most important piece of equipment you can bring with you, because they will be the only thing you will get to eat all day long. Be sure your parents make a good selection with things that people will like, like ham salad, ham salad, or ham salad. Throw the sandwiches into a leaky plastic bag and then put them in the cooler with a lot of ice and sodas to ensure freshness and just the right amount of dripping sogginess. Bring enough life jackets for all the people who'll be in the boat, but make sure you've only got two that anyone would actually want to be seen in. The rest should be ugly, smelly, moldy old things that you don't even want to touch. These will remain stoed in some remote corner of the boat where nobody could get to them if they were needed, because nobody wants to get caught dead in one, anyway. Make sure to bring along enough skis so that every single person in the boat, including the driver, could be out and skiing at the same time if need be. You never know when someone is going to want to double-, triple-, or octuple-ski, so it's best to be prepared for any eventuality. As an added benefit, you can use these extra skis to tile the floor of your boat so you don't ever have to walk on that icky waterproof carpeting. Don't worry about breaking the fins off the bottoms of the skis when you step on them. You don't really need those, anyway. Waterskis are a dime a dozen, so if you want, you can even toss them overboard after the day is done. You won't need sunscreen, as you'll be moving around a lot. When you're moving, most of the sun's harmful radiation misses you, so you won't get burnt.

Putting the Boat in the Water
This can be kind of tricky, which is why you should have your parents do it for you. If you are the parent, you should not go boating unless you have friends along who will do this stuff for you. Backing a trailer into a slip is difficult and could result in damage to your boat, vehicle, or person, so if possible, have your friends use their boats, vehicles, and persons. Have the most expendable person inside the boat while launching it, so that if it happens to fall off the trailer, hit the side of the slip, or do something else which causes it to explode, you won't have lost much in the way of human life. The person I most prefer for this task is my little brother, musicaljon.

Finding the right place to ski:
Find the place with the smoothest water with the most debris floating on top of it. If you want a fun challenge, find a place where old dead tree trunks rise up from the water. You can find these areas in most man-made lakes.

Slalom or standard?
I prefer to slalom ski. Mainly because as long as you're up, you look like a complete badass. There are all sorts of dorky positions you can wind up in while you're on two skis, but when you're on one ski, you're either cruising along with a wide spray of awesomeness trailing behind you, or you're DEAD. So, chicks either dig you (if that's what you're into) or you're not around to care about it anyway.

Tubing
A lot of people like to be pulled behind a boat in a big rubberinnertube. This is because, unlike most theme park rides, tubing can cause you severe, permanent bodily injury. This is especially fun for smaller children, because their bodies are made mostly of rubber and sugar, so they can take the punishment doled out by even the most ruthless boat driver. To find out what tubing feels like, imagine using your entire body to simulate the actions of a flag on a very windy day. And yes, your body can make that sound when you're laying on top of a tube being smashed into 1 meter waves.

Kneeboarding
Kneeboarding is a lot like tubing, only your knees take the punishment instead of your back and you're strapped in. Unfortunately, the board's natural position is with you upside down in the water, and this can be slightly disconcerting after a major crash when you're breathing in lungsful of water and desperately fumbling for the Velcro Strap of Death.

Driving the Boat
Always make it clear to other boaters that you have no idea where you're going. This is the best way to keep other boats as far away as possible from you, thus increasing safety. Go under bridges as fast as possible to clear the way for other boats to get through. Those "No Wake" signs are only meant for the floating funerals. If you see a bunch of guys fishing, drive as close to their boat as possible. This stirs up the fish and makes them hungrier, and thus easier to catch. Those fishermen will be thinking of you for the rest of the day!

Ending your Day
Again, have your parents/friend put the boat back on the trailer. This is why you brought them along. They're also helpful for unloading all the crap that's in the boat once you get home. No need to shower; lakewater is as good as any bathing you could ever do. Just feel all that extra body and sheen it's added to your hair!